One way audio when video is enabled

I have interesting problem on Asterisk 1.4. I have video enabled, and when I make a call Asterisk sends SIP INVITE with correct media attributes in SDP for audio and video. and the called party answers with 200OK but sets “c=” field at the session-level, that is for entire session, and one more contact “c=” for video, and sets it to

cuts from SDP in INVITE from Asterisk:

c=IN IP4
m=audio 13472 RTP/AVP 18 0 8 101
a=rtpmap:18 G729/8000
m=video 19808 RTP/AVP 99
a=rtpmap:99 H264/90000

and part from SDP of 200OK from the called server:

c=IN IP4
m=audio 60512 RTP/AVP 18 0 8 101
a=rtpmap:18 G729/8000
m=video 50000 RTP/AVP 99
c=IN IP4

So, as you see the called party sets “c” for entire session and video only, but for audio it stays unclear.

When I disable video everything works fine, it is obvious.

The SDP protocol says:

The “c=” field contains connection data.

A session announcement must contain one “c=” field in each media
description (see below) or a “c=” field at the session-level. It may
contain a session-level “c=” field and one additional “c=” field per
media description, in which case the per-media values override the
session-level settings for the relevant media.

but still it is not clear if there must be separate contact information for audio and video or no.